Epidemiologic studies of AD must be interpreted with recognition that results vary based on the diagnostic criteria used by the investigators. Despite such limitations, multiple studies suggest that the prevalence of AD has been increasing since World War II^[8]. Since 90% of patients with AD have disease onset before the age of 5 years, much of the prevalence data is derived from younger schoolchildren^[9]. Studies in the past decade have estimated the prevalence of AD to be 10% to 20% in schoolchildren from the US, northwest Europe, Australasia and some regions of Asia and South America; surveys conducted in Mediterranean countries, Eastern Europe and Africa have reported lower figures^[10–15]. The majority of population-based studies in schoolchildren demonstrate a slight, but reproducible, preponderance in girls^[13].

AD is thought to arise from an interaction between environmental and genetic factors. While parental (especially maternal) history of atopy was found to be one of the …